Rotatable and tunable heaters for semiconductor furnace

ABSTRACT

A method for forming a layer of material on a semiconductor wafer using a semiconductor furnace that includes a thermal reaction chamber having a heating system having a plurality of rotatable heaters for providing a heating zone with uniform temperature profile is provided. The method minimizes temperature variations within the thermal reaction chamber and promotes uniform thickness of the film deposited on the wafers.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of U.S. application Ser. No. 12/409,880filed Mar. 24, 2009, the entire disclosure of which is incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention generally relates to semiconductors, and moreparticularly to heating systems used in semiconductor furnaces for waferprocessing.

BACKGROUND

Modern semiconductor electronic device packages such as integratedcircuit (IC) chips are formed on a wafer by building multiple stackedlayers of materials and components on a semiconductor substrate. Asingle wafer will contain a plurality of individual ICs or dies, whichare later separated following fabrication by a cutting process referredto in the art as singulation or dicing. The semiconductor devicestypically incorporate numerous electrically active components which areformed in multiple layers of an electrically insulating or dielectricmaterial. Metal conductor interconnects, which may be made of copper insome embodiments, are formed by various additive patterning anddeposition processes such as damascene and dual damascene toelectrically couple the active components together in the various layersand to create circuit paths or traces within a single layer ofdielectric material. Modern semiconductor fabrication entails arepetitive sequence of process steps including material deposition(conductive and non-conductive dielectric materials), photolithographicpatterning of circuits in the dielectric material, and material removalsuch as etching and ashing which gradually build the stackedsemiconductor device structures.

Some of the foregoing semiconductor processing steps used in fabricatingsemiconductors specifically include oxidation, diffusion, doping,annealing, and chemical vapor deposition (CVD). These processes aretypically performed at elevated temperatures within heated controlledenvironments. CVD is a chemical vapor deposition process used to produceor deposit thin films of material on the wafer including withoutlimitation metals, silicon dioxide, tungsten, silicon nitride, siliconoxynitride, and various dielectrics. The CVD process entails placing awafer or plurality of wafers in a heated reaction chamber andintroducing one or more reactant gases into the chamber. The gasescontain with various chemical precursors (e.g. SiH2C12 and NH3 or silaneand NH3 to form a silicon nitride film) that react at the heated wafersurface to form a thin film of the desired semiconductor material andthickness thereon. The uniformity of the film deposited on the wafer byCVD is affected and controlled by regulating and attempting to optimizeCVD process parameters such as temperature of the wafer, reactionchamber pressure, flow path and rate of reactant gases, and depositiontime or duration.

One type of heated or thermal reaction chamber used in CVD processes arevertical semiconductor furnaces. These vertical furnaces are capable ofholding a plurality of vertically-stacked semiconductor wafers whichundergo CVD batch processing simultaneously. The vertical furnacesinclude a thermal reaction vessel or chamber which may be loaded withmultiple wafers that in some embodiments are held in avertically-stackable rack referred to in the art as a wafer ladder orboat. The wafer boat comprises a frame having multiple horizontal slotswhich each hold an individual wafer in spaced-apart, stacked verticalrelationship to the other wafers. The wafer boats may typically holdfrom approximately 50-125 wafers. Vertical space is provided between thewafers to allow the CVD reactant gases to circulate therethrough forforming the desired material film deposits on top of the wafers. Thethermal reaction chambers are commonly cylindrical in shape (alsoreferred to as reaction tubes) and generally have a closed top and openbottom to allow for insertion of the wafer boats holding the verticalwafer stacks.

The thermal reaction chambers, wafer boats or racks, and othercomponents that may be exposed to the heat and corrosive gases arecommonly made of quartz or SiC to withstand CVD process temperaturesthat may range from about 200-1200 degrees C. in some applicationsdepending on the type of semiconductor material film to be deposited onthe wafers.

The wafer boats may be disposed on an openable/closeable lid assemblywhich forms a bottom closure and platform for supporting the wafer boat.The lid assembly is configured and adapted to temporarily attach to andseal the bottom of the reaction chamber to form a gas-tight temporaryconnection during CVD processing. The lid assembly may be mounted on avertical elevator or lift which is operable to raise and lower the waferboat into and from the reaction chamber. The reaction chamber andassociated assembly typically includes a gas manifold with gas inletsand gas outlets for introducing and removing CVD process reactant gasesfrom the reaction chamber. A means for rotating the wafer boat andwafers held therein when the boat is positioned in the reaction chambermay be provided to promote uniform gas flow and heating throughout thewafer stack.

Some examples of conventional vertical semiconductor furnaces andassociated appurtenances are shown in U.S. Pat. Nos. 6,538,237;6,435,865; 6,187,102; 6,031,205; and 7,241,701; all of which areincorporated herein by reference in their entireties.

The vertical semiconductor furnaces include a heat source, which in someembodiments may include resistance type heaters, radiant type heaters,or a combination thereof. Examples of resistance type heaters includeelectric resistive wire coil elements or similar. Some examples ofradiant type heaters include heating lamps or quartz-heating elements.The heaters are typically disposed outside but proximate to the quartzreaction chamber to heat the chamber and increase its internaltemperature.

In order to improve manufacturing efficiencies and reduce productioncosts, wafer sizes have steadily increased over the years. Standardsilicon wafer sizes have steadily grown from about 200 mm (about 8inches diameter) to 300 mm (about 12 inches diameter). The nextgeneration wafer standard has been set for 450 mm (about 18 inches indiameter). The next generation wafer size of 450 mm has created achallenge in maintaining a uniform temperature in the vertical waferstacks throughout the wafer boat during the CVD process that is desiredto promote uniform material film deposition on each wafer's surface.

Existing heater arrangements used in CVD thermal reaction chambers haveproven to be inadequate to provide the needed uniformity in temperaturefor maintaining the desired consistency in both material film thicknessdeposited over the entire surface of each individual wafer, and fromwafer-to-wafer throughout the entire batch or stack of wafers beingprocessed for the larger next generation wafer sizes. Ideally, eachwafer in the entire batch of wafers undergoing CVD in the thermalreaction chamber should have a uniform film thickness in order to meetacceptable process thickness variation tolerances on an individual waferand wafer-to-wafer basis. Some existing heater arrangements used fortraditionally smaller 200-300 mm diameter wafers do not provide thenecessary temperature control and uniformity to maintain the desiredtolerances for 450 mm wafers. Horizontal temperature variation betweenthe edges and center of the wafers cause generally unacceptablevariances in layer thicknesses deposited on each wafer. Temperatures atthe wafer center are typically lower than at the edges. Verticaltemperature variations in the stack of wafers held by the wafer boatcause generally unacceptable variances in layer thicknesses depositedfrom wafer-to-wafer in the stack.

An improved heater arrangement for vertical semiconductor furnaces isdesired to meet the challenges of the next generation wafer size.

SUMMARY

According to one embodiment, a semiconductor furnace suitable forchemical vapor deposition wafer processing includes a vertical thermalreaction chamber having a sidewall defining a height, a top, a bottom,and an internal cavity for removable holding a batch of wafers. Thesemiconductor furnace further includes a wafer boat positioned in thereaction chamber being configured and adapted to hold a plurality ofwafers in vertically-stacked relationship, and a heating systemcomprising a plurality of sidewall heaters spaced along the height ofthe reaction chamber which are arranged and operative to heat thechamber. The heating system includes user-adjustable sidewall heaterspacing and sidewall heater rotation with variable rotational speed anddirection being adjustable for each heater. The function of heaterrotation is preferably independent for each heater and the tuning oradjustment of heater spacing is independent in some embodiments.Advantageously, the foregoing heater system promotes uniform wafer filmdeposit thickness on each wafer and from wafer-to-wafer in each batchprocessed in the semiconductor furnace by providing more flexibility totune temperature profiles to get desired temperature and/or waferuniformity.

According to another embodiment, a semiconductor furnace includes avertical thermal reaction chamber having a sidewall defining height andan internal cavity for removably holding a batch of wafers. Thesemiconductor furnace further includes a wafer boat positionable in thereaction chamber being configured and adapted to hold a plurality ofwafers in vertically-stacked relationship. A heating system is providedthat includes a plurality of rotatable sidewall heaters spaced along theheight of the reaction chamber. The sidewall heaters are rotatable withrespect to the reaction chamber about a rotational axis. The sidewallheaters define a plurality of sidewall heater zones in the reactionchamber that are vertically spaced along the height of the reactionchamber with temperature in each heater zone being controlled by arespective sidewall heater. In one embodiment, the sidewall heater zonesare adjustable in vertical position with respect to the reactionchamber.

According to another embodiment, a semiconductor furnace includes: avertical thermal reaction chamber having a sidewall defining a heightand an internal cavity for removably holding a batch of wafers. Thesemiconductor furnace further includes a wafer boat positionable in thereaction chamber being configured and adapted to hold a plurality ofwafers in vertically-stacked relationship. A heating system is providedthat includes a plurality of sidewall heaters spaced vertically alongthe height of the reaction chamber. In this embodiment, the spacingbetween the sidewall heaters is adjustable for optimizing temperatureprofiles within the reaction chamber.

A method for forming a layer of material on a semiconductor wafer isprovided. The method includes providing a semiconductor furnaceincluding a vertical thermal reaction chamber having a sidewall defininga height and an internal cavity for removably holding a batch of wafers.The semiconductor furnace further includes a heating system comprising aplurality of rotatable sidewall heaters spaced along the height of thereaction chamber. The method further includes inserting a wafer boatholding a plurality of vertically-stacked wafers into the reactionchamber, rotating at least one of the sidewall heaters with respect tothe reaction chamber; and forming a film of material on each wafer viachemical vapor deposition. In some embodiments, the method furtherincludes a step of raising or lowering at least one of the sidewallheaters with respect to the reaction chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the preferred embodiments will be described withreference to the following drawings where like elements are labeledsimilarly, and in which:

FIG. 1 is a schematic cross-sectional side view of a first existingheater arrangement for a semiconductor furnace;

FIG. 2 is a schematic cross-sectional side view of a second existingheater arrangement for a semiconductor furnace;

FIG. 3 is a schematic cross-sectional side view diagram of a heaterarrangement for a semiconductor furnace according to one embodiment ofthe present invention;

FIG. 4 is a perspective side view of sidewall heaters according to oneembodiment of the semiconductor furnace of FIG. 3;

FIG. 5 is a perspective side view of a sidewall heater according to oneembodiment of the semiconductor furnace of FIG. 3; and

FIG. 6 is a view of a sidewall heater according to one embodiment of thesemiconductor furnace of FIG. 3.

All drawings are schematic and are not drawn to scale.

DETAILED DESCRIPTION

This description of illustrative embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description. In the description ofembodiments disclosed herein, any reference to direction or orientationis merely intended for convenience of description and is not intended inany way to limit the scope of the present invention. Relative terms suchas “lower,” “upper,” “horizontal,” “vertical,”, “above,” “below,” “up,”“down,” “top” and “bottom” as well as derivative thereof (e.g.,“horizontally,” “downwardly,” “upwardly,” etc.) should be construed torefer to the orientation as then described or as shown in the drawingunder discussion. These relative terms are for convenience ofdescription only and do not require that the apparatus be constructed oroperated in a particular orientation. Terms such as “attached,”“affixed,” “connected” and “interconnected,” refer to a relationshipwherein structures are secured or attached to one another eitherdirectly or indirectly through intervening structures, as well as bothmovable or rigid attachments or relationships, unless expresslydescribed otherwise. Moreover, the features and benefits of theinvention are illustrated by reference to the preferred embodiments.Accordingly, the invention expressly should not be limited to suchpreferred embodiments illustrating some possible non-limitingcombination of features that may exist alone or in other combinations offeatures; the scope of the invention being defined by the claimsappended hereto.

FIGS. 1 and 2 show schematic diagrams of two conventional heaterarrangements used for semiconductor furnaces that process traditionalwafer sizes of 300 mm or less. In FIG. 1, there are five sidewall heaterzones provided at the sidewall of the CVD reaction chamber. Each heaterzone is defined by and includes a heater, which in some embodiments isan electric resistance type heater coil or element. An alternativeconventional heater arrangement shown in FIG. 2 includes three sidewallheater zones provided at the sidewall of reaction chamber, one topheater zone, and one bottom heater zone. Conventional electric orelectronic heater controls are provided in both of the foregoing heaterarrangements that allows the temperature output from each heater to beadjusted by varying the energy input from the electrical power source.

The sidewall heater zones established for the existing heaterarrangements shown in FIGS. 1 and 2 are fixed because the sidewallheaters are fixed or stationary in position in relation to the reactionchamber. Accordingly, the vertical spacing between the sidewall heaterscannot be adjusted. In addition, although the wafer boat and wafersretained thereon may be rotated during CVD processing in thesemiconductor furnace, the sidewall heaters themselves are typicallystationary and cannot be rotated. Therefore, there is little ability tofine tune the sidewall temperature zones and temperature profiles withinthe reaction chamber with these existing heater arrangements.

When either of these foregoing arrangements is used for CVD processingof the larger next generation 450 mm size wafer, the temperatureprofiles can be improved and optimized according to the presentinvention through heater rotation and/or heater spacing adjustmentbetween the sidewall heaters. Fine tuning sidewall heater rotation speedand spacing of the heaters provides more adjustable parameters to tuneand obtain the desired process temperature profile with reaction chamber20.

FIG. 3 is a schematic diagram of one embodiment of a semiconductorprocessing furnace 10 or tool incorporating a CVD thermal reactionchamber 20 according to the present invention. Semiconductor furnace 10may include a conventional insulated housing 12 (partially shown in FIG.3) which is configured and adapted to provide a thermal enclosure aroundsubstantially all of reaction chamber 20 to establish a temperaturecontrolled environment for reaction chamber 20. CVD reaction chamber 20includes an internal cavity 21 defining a space for removably receivinga conventional wafer boat 22 that is configured and adapted forsupporting and holding a plurality of vertically-stacked wafers W in aconventional manner. In one embodiment, reaction chamber 20 may have aclosed top 23, sidewall 24, and open bottom 25 to allow the wafer boat22 to be inserted and removed from the chamber for batch processing ofwafers W. In one embodiment, wafer boat 22 comprises a conventionalopen-frame structure such as a ladder-type design having multiplehorizontal slots for supporting the wafers W and allowing reactant gasto flow horizontally over the face of the wafers W to build the desiredmaterial film thicknesses thereon. Wafer boat 22 may be sized to hold50-125 wafers W or more in some embodiments; however, any suitablenumber of wafers may be held by the wafer boat depending on the heightof the reaction chamber 20 provided. In some representative embodiments,typical vertical spacing of wafers W in wafer boat 22 may be around 6 to10 mm. Wafer boat 22 may be made of quartz or any other suitablematerial commonly used in the art.

Reaction chamber 20 may have a conventional cylindrical shape in oneembodiment and may be made of quartz or SiC. Reaction chamber 20 mayinclude a coating such as polysilicon or another coating materialtypically used depending on the type of process conducted in thechamber. Reaction chamber 20 may have any suitable height or lengthdepending on the number of wafers to be processed in each batch. In someexemplary embodiments, reaction chamber 20 may have a representativevertical height or length of 100-150 cm; however, any suitable height orlength may be provided. In some representative embodiments, reactionchamber 20 for processing 450 mm wafers may be sized to be more than 450mm diameter and a chamber length of about 50 to 200 cm depending on thenumber of wafers to be processed simultaneously in the chamber.

A sealable and openable bottom closure lid 26 is provided which may besealed to the bottom 25 of reaction chamber 20 to form a gas-tightchamber seal for processing the wafers W. In one embodiment, bottom 25may be provided with a flange as shown for receiving lid 26. Bottomclosure lid 26 may include a support structure to provide support forwafer boat 22 which may be attached to the lid in a conventional manner.

Other conventional appurtenances typically used in conjunction with CVDreaction chamber 20 processing assemblies and semiconductor furnaces maybe provided. For example, reaction gas supply inlet connections 30 andoutlet connections 31 may be furnished to allow one or more processgases to be introduced and removed from reaction chamber 20. Gasmanifold and injectors, furnace cooling to allow quick changing of waferbatches, an external insulated housing enclosing the reaction chamber20, wafer boat elevator or lift and robotically-controlled arm forpositioning, raising, and lowering the wafer boat 22 into/from chamber20, etc. (not shown). Some of these appurtenances which may be providedare described, for example, in U.S. Pat. Nos. 6,538,237; 6,435,865;6,031,205; and 7,241,701; which are all incorporated herein by referencein their entireties.

In some embodiments, wafer boat 20 may be provided with a conventionalmotor drive mechanism (not shown) to allow the stack of wafers W to berotated (see rotational arrow in FIG. 3) during the CVD process topromote uniform thickness of the layer of material deposited on thewafers.

The operation of semiconductor furnace 10 and batch processing of wafersW may be controlled by a suitable commercially-available temperaturecontrollers as conventionally used in the art to regulate the heatoutput from the furnace heating system including temperature ramp up andramp down rates.

With continuing reference to FIG. 3, semiconductor furnace 10 includes aplurality of heaters, which preferably are distributed along thesidewall 24, top 23, and bottom 25 of CVD reaction chamber 20. In oneembodiment, the heaters include sidewall heaters 40A-40F, top heaters41, and bottom heaters 42 as shown.

To provide better temperature control and uniform heat distributionthroughout the reaction chamber 20 for CVD processing of next generation450 mm diameter or larger wafers, sidewall heaters 40A-40F in oneembodiment are preferably rotatable about a rotational axis RA inrelation to reaction chamber 20 as shown in FIG. 3 and further describedherein. In one embodiment, rotational axis RA may be axially alignedwith the vertical axis or centerline of reaction chamber 20. Thesidewall heaters 40A-40F may be independently rotatable in someembodiments, and in other embodiments may be rotatable in unison.Sidewall heaters 40A-40F may be rotatable in a rotational direction, andat varying rotational speeds.

The rotational speed and direction of sidewall heaters 40A-40F arepreferably user-adjustable either manually or via a computer controller.In one embodiment, therefore, heater rotation may be controlled via arotation motor controller and a rotation control signal coming from amotor encoder and close loop control. The rotation motor controller mayexecute appropriately configured programmable control logic or softwareto automatically adjust the rotational direction and speed of sidewallheaters 40A-40F. Preferably, sidewall heaters 40A-40F are rotatableindependently of the ability to rotate wafer boat 22 and wafers Wtherein which may be provided in some embodiments.

In other embodiments, the vertical spacing or distance D between eachsidewall heaters 40A-40F may be also be adjustable as further describedherein to provide the ability to further fine tune the temperatureprofile within the reaction chamber 20 closer to the desired targettemperature profile. Each sidewall heater 40A-40F defines acorresponding heater zone Z as shown in FIG. 3. In some embodiments,therefore, sidewall heaters 40A-40F may be either rotatable, adjustablein vertical distance D, or a combination of both depending on the CVDprocess temperature control requirements.

The spacing between sidewall heaters 40A-40F are preferablyuser-adjustable either manually or via a computer controller. In oneembodiment, therefore, heater spacing may be controlled by a spacingmotor controller and a spacing control signal coming from a motorencoder and close loop control. The spacing motor controller may executeappropriately configured programmable control logic or software toautomatically adjust the spacing between the sidewall heaters 40A-40Fand relative vertical position of each heater with respect to reactionchamber 20.

In one embodiment, the number of sidewall heaters 40A-40F that arefurnished may be selected such that each sidewall heater controlstemperature for less than or equal to no more than ten (10)vertically-stacked wafers W per heater to provide better temperatureuniformity and corresponding uniformity in wafer level thicknesses bothon each wafer W (e.g. from center of wafer to edges thereof) and fromwafer-to-wafer in the vertical stack of wafers W supported by the waferboat 22. This arrangement may further enhance the ability to control CVDprocess temperature profiles within the reaction chamber 20 close to thedesired target profiles.

In some embodiments, the sidewall heaters 40A-40F and heater zones Z maybe approximately evenly distributed along the vertical height of thereaction chamber with preferably each heater controlling temperaturewithin a respective heater zone having no more than 10vertically-stacked wafers W.

With continuing reference to FIG. 3, sidewall heaters 40A-40F in oneembodiment may be electric resistance type heaters having controllableheat output which may be regulated by adjusting the energy input to eachheater via a variable resistance control such as a rheostat or othersuitable similar electrical control device commonly used in the art.Sidewall heaters 40A-40F are preferably disposed proximate to theexternal sidewall 24 and are arranged in spaced vertical relationship toeach other along the height of reaction chamber 20. Sidewall heaters40A-40F therefore define a plurality of vertical heater zones Z withinreaction chamber 20 with the temperature in each zone being controlledby heaters 40A-40F.

The heat output from sidewall heaters 40A-40F may be adjusted and finetuned to control the temperature in each heater zone Z. The heat outputfrom each sidewall heaters 40A-40F preferably is adjustable independentof the other sidewall heaters. The heat output setting of each sidewallheater may be adjusted either manually by a user or automatically via aheater controller or computer in conjunction with control signalsgenerated by temperature sensors disposed in the semiconductor furnace10 and/or based on predetermined heater temperature output settingsderived from experience and empirical data correlated with the size ofwafer being processed and/or type of material film being deposited onthe wafers W.

In one embodiment, sidewall heaters 40A-40F may each include one or moreconventional electric resistance coils or elements as further describedherein that are disposed circumferentially around sidewall of reactionchamber 20 at the outer circumference of reaction chamber 20. Sidewallheaters 40A-40F preferably extend around the entire circumference ofreaction chamber 20. FIG. 3 diagrammatically shows the left and rightportions of each sidewall heater 40A-40F. The electric resistance coilsare electrically coupled via conventional conductors to an electricalpower supply, which may be routed through suitable conventional variableresistance electrical controls as typically used in the industry toallow the heat output (e.g. Btuh) to be adjusted from each heater40A-40F.

FIGS. 4 and 5 show one possible embodiment of sidewall heaters 40A-40Faccording to the present invention. In this figure, a portion ofsemiconductor furnace 10 is shown with three sidewall heaters 40A, 40B,and 40C. Each sidewall heater 40A-40F includes an annular orcylindrically-shaped rotary heater base 50 that may contain one or moreelectric resistance heater coils or elements 51 preferably mounted on aninward facing interior side of the rotating base. Each sidewall heater40A-40F defines a respective heater zone Z (see FIG. 3).

According to another aspect of the invention, as further describedherein, rotary heater base 50 may be rotatably mounted in an outersupport base 60 which is vertically adjustable in position to allow thespacing or distance D between each rotating base 50 to be adjusted. In apreferred embodiment, support base 60 is preferably supported from anyportion semiconductor furnace 10 such as housing 12. Preferably, supportbase 60 is not rotatable with respect to reaction chamber 20 or housing12, but is vertically adjustable in position with respect to chamber 20.

Referring now to FIG. 4, sidewall heaters 40A, 40B, and 40C may eachcomprise individual annular-shaped coils or elements 51 that areorientated horizontally with respect to vertical reaction chamber 20.Any suitable configuration, number, and arrangement of electrical heatercoils 51 may be used so long as sufficient heat distribution andtemperature control is provided. The configuration, number, andarrangement of electrical heater coils 51 therefore will be dictated bythe process heating requirements and size of the reaction chamber 20.Accordingly, in some other possible embodiments (not shown), electricheater coil 51 may be configured as a single spiral-shaped elementextending helically upwards on the interior side of rotating heater base50 from the bottom to top of the heater base. In yet other possibleembodiments (not shown), heater coil or coils 51 may comprise aplurality of vertically-aligned individual elements disposed on theinterior side of rotating heater base 50.

Electric heater coils 51 may be mounted to rotating heater bases 50 byany suitable conventional attachment means. Preferably, rotating heaterbases 50 are not rigidly mounted to furnace housing 10 to allow thebases to be rotated with respect to reaction chamber 20 andsemiconductor furnace housing 10 as further described herein.

Referring to FIGS. 4 and 5, rotating heater bases 50 are preferablycylindrical in shape in one embodiment and have a diameter larger thanreaction chamber 20 to allow the heater base to extend circumferentiallyaround the reaction chamber. In a preferred embodiment, rotating heaterbases 50 include an external gear ring 72 disposed on an outer surfacethereof for rotating the heater base. Gear ring 72 is annular in shapeand extends around the circumference of rotating heater base 50 and isoriented perpendicular to rotational axis RA (see FIG. 3).

In one possible embodiment, gear ring 72 may be formed directly on anouter surface of rotating heater base 50. In other embodiments, gearring 72 may be formed on a separate collar that may be attached to anouter surface of rotating heater base 50 by any suitable manner commonlyused in the art such as with mechanical fasteners, adhesives, welding,shrink or press fitting, etc.

Gear ring 72 may include any suitable type or style of conventional gearteeth and may be for example a spur gear or a helical gear in someexemplary embodiments. Gear ring 72 is configured and adapted to bedriven by a complementary-configured motor-driven gear drive 73. Geardrive 73 includes a motor 71 and gear 70 coupled to a motor shaft. Gear70 is configured and adapted to mesh with gear ring 72 on rotatingheater base 50. such that gear 70 and gear ring 72 have matching stylesof gear teeth in a preferred embodiment (e.g. spur or helical gears).Gear drive 73 may be any commercially-available drive unit with suitablehorsepower and output torque to rotate sidewall heaters 40A-40F.

In one possible embodiment, gear drive 73 may be mounted to outersupport base 60 as shown in FIGS. 4 and 5. In other possibleembodiments, gear drive 73 may be mounted to any portion ofsemiconductor furnace 10. In either embodiment, a window 61 is providedthat extends completely through support base 60 to allow gear 70 toengage gear ring 72 on rotating heater base 50 as shown in FIG. 5. Thevertical extent of window 61 depends on whether gear drive 73 is mountedto support base 60 or a part of furnace 10.

In the first embodiment, referring to FIG. 5 where gear drive 73 ismounted directly to support base 60, window 61 need only have a heightsufficient to allow the thickness T1 of gear 70 to extend through thewindow to mesh with gear ring 72. Both rotating heater base 50 and geardrive 73 remain in the same relative vertical positions when supportbase is vertically moved upwards or downwards to adjust the space ordistance D between pairs of sidewall heaters 40A-40F. In this case, gearring 72 need only have a vertical thickness T1 approximately equal tovertical thickness T2 of gear 70 of gear drive 73.

In the second embodiment where gear drive 73 is mounted to furnace 10(not shown), window 61 requires a height large enough to accommodate themaximum distance that is provided for adjusting the vertical position ofsupport base 60. In this case, gear ring 72 must have a thickness T1that is larger than thickness T2 of gear 70 of gear drive 73 because thegear drive does not move with upwards/downwards with support base 60 androtating heater base 50. Therefore gear 70 will slide up/down on gearring 72 which is attached to and remains stationary relative to rotatingheater base 50. adjustment

Support base 60 preferably rotatably supports rotating heater base 50such that base 50 may be rotated with respect to support base 60 andreaction chamber 20. Referring to FIGS. 4-6, support base 60 may becylindrical in shape having a sleeve-like structure that surroundsrotating heater base 50. Support base 60 is preferably concentricallyaligned with rotating heater base 50 disposed therein and chamber 20disposed inside base 50. An annular gap of sufficient size separatessupport base 60, rotating heater base 50, and reaction chamber 20 toallow base 50 to freely rotate without binding support base 50 orreaction chamber 20. In one possible embodiment, the rotating heaterbase 50 is mounted with outer support base 60, and the interface betweenbases 50 and 60 is a metal fluid seal (ring type seal); the base 50 canbe rotated independently by itself by motor drive 73.

Referring to FIGS. 3-5, to provide the capability of fine tuning oradjusting the spacing or distance D between the sidewall heaters40A-40F, an outer surface of support base 60 may include a spiral orhelical gear thread or tooth 82 in one embodiment that is disposedthereon. Helical tooth 82 extends in a full 360 degree helical patternaround the outer circumference of support base 60 and extendslongitudinally along at least a portion of the height of outer supportsleeve 60. The vertical length of helical tooth 82 will determine themaximum range of vertical adjustment for each support base 60 andcorrespondingly each sidewall heaters 40A-40F. Helical tooth 82resembles a worm gear formed around the outer circumference of supportbase 60 and meshes with a complementary-configured gear teeth on gear 80of a second gear drive 83 as shown in FIGS. 4-5. Gear 80 of gear drive83 may be any suitable type of gear including for example withoutlimitation a helical gear or spur gear depending on the size and pitchof helical tooth 82 provided. Preferably, when a helical gear is usedfor gear 80, teeth on gear 80 are of the same hand or orientation ashelical tooth 82 on outer support base 60 (i.e., right hand or left handteeth).

In one preferred embodiment, gear drive 83 may be supported and mountedto semiconductor furnace 10, and more preferably housing 12 or anotherportion of the furnace or its related appurtenances and structure. Outersupport base 60 is preferably not rigidly mounted to semiconductorfurnace 10 to allow support base 60 (with rotating heater base 50disposed therein) to be moved in raising and lowering motions withrespect to the furnace

In one possible embodiment, helical tooth 82 may be formed directly onan outer surface of support base 60. In other embodiments, helical tooth82 may be formed on a separate collar that may be attached to an outersurface of support base 60 in any suitable manner commonly used in theart such as by mechanical fasteners, adhesives, welding, shrink or pressfitting, etc.

In other possible alternative embodiments (not shown), support base 60may include a rack and pinion mechanism in lieu of a using helical geartooth 82. Accordingly, an elongated gear rack may be arranged verticallyon an outer surface of the support base that extends parallel torotational axis RA (see FIG. 3) and which meshes with a suitablyconfigured gear 80 provided with gear drive 83. In one embodimentpossible embodiment, gear 80 may be a spur gear. Gear drive 83 providesraising and lowering motions to support sleeve 60 allowing the distanceD between sidewall heaters. 40A-40F to be adjusted and positioned tofine tune the temperature profile within reaction chamber 20. The outersupport base 60 is preferably carried by furnace or tool housing 12 androtated by outside rotating motor gear drive 83 as described herein.

Rotating heater bases 50 may be made of any suitable material capable ofwithstanding the temperatures produced by the heater coils 51 attachedthereto. In some representative embodiments, heater bases 50 maypreferably be made of stainless steel. Outer support bases 60 may bemade of any suitable material capable of withstanding the temperaturesproduced within the semiconductor furnace 10. In some representativeembodiments, support bases 60 may preferably be made of stainless steel.

An exemplary method of operating semiconductor furnace 10 and sidewallheaters 40A-40F will now be provided. Referring to FIGS. 3-6, the methodin one possible includes inserting wafer boat 22 holding a plurality ofwafers W into reaction chamber 20 (see FIG. 3) and closing bottomclosure lid 26 to seal the reaction chamber.

With continuing reference to FIGS. 3-6, the following steps may beperformed in any suitable sequence. Sidewall heaters 40A-40F areenergized to power electric coils or elements 51 and generate heat toheat reaction chamber 20. Gear drives 73 may be energized to rotatesidewall heaters 40A-40F, and more specifically rotating heater bases 50engaged by gear 70 of gear drives 73. Preferably, the speed of rotationand/or direction of rotation are independently adjustable for eachsidewall heater 40A-40F.

Depending on actual process temperatures monitored in reaction chamber20 by temperature sensors or past experience in operating thesemiconductor furnace 10 for a given CVD process being performed, methodmay include adjusting the vertical spacing or distance D between some orall of the sidewall heaters 40A-40F to fine tune and optimize thetemperature profiles within reaction chamber 20. This may beaccomplished by energizing gear drives 83 and raising or lowering outersupport bases 60 (supporting and housing rotating heater bases 50therein) of one or more sidewall heaters 40A-40F; the support bases 60being engaged with gear 80 of these gear drives. Preferably, thesemiconductor furnace 10 and gear drives are arranged so that thevertical position of each heater base 50 corresponding to one of thesidewall heaters 40A-40F is independently adjustable from the otherssince not all sidewall heaters will necessarily require adjustment tooptimize the temperature profile within reaction chamber 20 in everyinstance. Wafers W may then undergo the desired CVD processing byinjecting the appropriate reactant bases into reaction chamber 20. Insome embodiments, wafer boat 22 may be rotated by conventional boatdrives known to those skilled in the art to further enhance wafertemperature profiles and uniformity in material films deposited on thewafers.

Advantageously, the foregoing method and sidewall heater mechanismimproves temperature profile control within the reaction chamber 20 andpromotes more uniform film thicknesses deposited on each wafers and fromwafer-to-wafer in the process batch during CVD. The electricalresistance of each heater coil or element 51 changes from location tolocation on each coil after repeated use over a period of time, therebycreating non-uniformity in power and heat output from each coil that maycontribute to non-uniform heating of the reaction chamber 20 processingenvironment. The rotating heater bases 50 are intended to improve thetemperature uniformity in the reaction chamber 20 and across each waferrequired for uniform film deposits on the wafers. Since each heater coil51 may exhibit different levels of such electrical resistance changes,the present invention advantageously provides the ability toindependently adjust rotational speed and/or direction for each of thesidewall heaters 40A-40F.

Referring to FIG. 3, top heaters 41 may be a bulk shaped electricresistance coils or elements and heater shaped may be varied which baseon temperature requirement. Preferably, at least two top heaters 41 andmore preferably at least three top heaters are provided to uniform CVDprocess temperatures in the bottom portion of the reaction chamber 20.Bottom heaters 42 may be a bulk shaped electric resistance coils orelements and heater shaped may be varied based on temperaturerequirements. Preferably, at least two bottom heaters 42 and morepreferably at least three bottom heaters are provided to uniform CVDprocess temperatures in the bottom portion of the reaction chamber 20.The top and bottom heaters cannot be rotated in some embodiments. Theheat output from each top and bottom heater 41, 42 is preferablycontrollable independently in a conventional manner similar to thatdescribed herein for sidewall heaters 40A-40F to allow the temperaturesin the top and bottom heater zones of reaction chamber 20 to be finetuned for optimum CVD processing and minimal variation in film thicknesson the wafers.

The wafer film thickness deposition rates are directly proportional toCVD process temperature and reactant gas ratio. Accordingly, precisecontrol of process temperatures within reaction chamber 20 to themaximum extent possible is desirable to minimize variation in filmthicknesses deposited by CVD on an individual wafer and wafer-to-waferbasis. Optimally, uniform film thickness is required so that all diesfabricated on each wafer and all dies in the batch from wafer-to-waferpossess the same mechanical, electrical, and reliability properties. Ifvariations in film thicknesses become too large, subsequentsemiconductor processing steps as the dies undergo layer-by-layerfabrication through a series of further material deposition and removalsteps may be adversely affected as well as the final die integrity. Inaddition, die failure rates may increase in subsequent wafer level andknown good die testing.

Typical CVD process temperatures may vary from about 200-800 degrees C.depending on the type of material to be deposited on the wafers W.During the CVD process, reactant gas is introduced to reaction chamber20 via the gas inlet connection 30, circulates through the reactionchamber and stack of multiple wafers, and exits the reaction chamberthrough gas outlet connection 31 as shown in FIG. 3.

Some gases may need to be preheated before entering the reactionchamber. Conventional gas preheating may be provided in some embodimentsby use of tape heater upon gas inlet pipes. The heat input by the tapeheaters are preferably controllable. These practices are well known tothose skilled in the art.

Embodiments of the sidewall heaters of the present invention aredifferent than conventional heaters which typically are fixed inposition and cannot be rotated or adjusted in vertical position withrespect to the reaction chamber. The present invention thereforeadvantageously provides heater rotating and spacing adjustment functionsfor obtaining more parameters that may be adjusted to tune temperatureto desired processing profiles.

While the foregoing description and drawings represent preferred orexemplary embodiments of the present invention, it will be understoodthat various additions, modifications and substitutions may be madetherein without departing from the spirit and scope and range ofequivalents of the accompanying claims. In particular, it will be clearto those skilled in the art that the present invention may be embodiedin other forms, structures, arrangements, proportions, sizes, and withother elements, materials, and components, without departing from thespirit or essential characteristics thereof. In addition, numerousvariations in the methods/processes and/or control logic as applicabledescribed herein may be made without departing from the spirit of theinvention. One skilled in the art will further appreciate that theinvention may be used with many modifications of structure, arrangement,proportions, sizes, materials, and components and otherwise, used in thepractice of the invention, which are particularly adapted to specificenvironments and operative requirements without departing from theprinciples of the present invention. The presently disclosed embodimentsare therefore to be considered in all respects as illustrative and notrestrictive, the scope of the invention being defined by the appendedclaims and equivalents thereof, and not limited to the foregoingdescription or embodiments. Rather, the appended claims should beconstrued broadly, to include other variants and embodiments of theinvention, which may be made by those skilled in the art withoutdeparting from the scope and range of equivalents of the invention.

What is claimed is:
 1. A method for forming a layer of material on asemiconductor wafer comprising: (a) providing a semiconductor furnacecomprising: a vertical thermal reaction chamber for processing a batchof wafers, said vertical thermal reaction chamber having a sidewalldefining a height and an internal cavity for removably holding the batchof wafers; a wafer boat positionable in the vertical thermal reactionchamber and being configured and adapted to hold a plurality of wafersin vertically-stacked relationship; and a heating system comprising: aplurality of rotatable sidewall heaters spaced along the height of thereaction chamber, whereby heating by the rotatable sidewall heatersresults in a temperature profile within the vertical thermal reactionchamber, the sidewall heaters being rotatable with respect to thevertical thermal reaction chamber about a rotational axis, wherein eachsidewall heater is provided on an annular rotating heater base having agear ring disposed thereon; a motor-driven gear drive provided for eachof the plurality of sidewall heaters, said motor-driven gear driveengaging the gear ring for rotating the annular rotating heater base andthereby controllably rotating the sidewall heaters for controlling thetemperature profile within the vertical thermal reaction chamber whilethe batch of wafers are being processed in the vertical thermal reactionchamber; and a motor controller for controlling the rotation of thesidewall heaters; (b) inserting a wafer boat holding a plurality ofvertically-stacked wafers into the vertical thermal reaction chamber;(c) rotating at least one of the rotatable sidewall heaters with respectto the vertical thermal reaction chamber, thereby forming a film ofmaterial on each wafer.
 2. The method of claim 1, further comprising astep of raising or lowering at least one of the rotatable sidewallheaters with respect to the vertical thermal reaction chamber, therebyadjusting the rotatable sidewall heater's vertical position.
 3. Themethod of claim 1, wherein the heating system further comprising: anouter annular support base for each of the annular rotating heater base,said outer annular support base having a vertical position with respectto the vertical thermal reaction chamber and rotationally supporting theannular rotating heater base, said annular support base having a helicalgear thread provided around the outer circumference of the support base;and a second motor-driven gear drive for each of the annular supportbase, wherein the motor-driven gear drive engages the helical gearthread of the annular support base for controllably adjusting thevertical position of the support base.
 4. The method of claim 3, furthercomprising a step of raising or lowering at least one of the annularsupport base using the second motor-driven gear drive, thereby adjustingthe vertical position of the support base which in turn adjusting therotatable sidewall heater's vertical position.
 5. The method of claim 1,wherein the heating system further comprising: an outer annular supportbase for each of the annular rotating heater base, said outer annularsupport base having a vertical position with respect to the verticalthermal reaction chamber and rotationally supporting the annularrotating heater base, said annular support base having a helical gearthread provided around the outer circumference of the support base; anda second gear drive for each of the annular support base, wherein thegear drive engages the helical gear thread of the annular support basefor controllably adjusting the vertical position of the support base. 6.The method of claim 5, further comprising a step of raising or loweringat least one of the annular support base using the second gear drive,thereby adjusting the vertical position of the support base which inturn adjusting the rotatable sidewall heater's vertical position.